Your compressor won't really notice or care whether the device is open or not. Bauer is a German company and has to comply with CE so they have a changeover device option to allow you to fill both types of tank valves off of the same compressor. We do not use these in the US and our DIN whips look exactly like a regulator din connection which is universal. They use short DIN for 200bar which will not screw into a 300bar valve because it only has 5 threads instead of 7 so it won't seat, and their 300bar whips have a nipple on the end that prevents them from seating into a 200bar valve. In Europe, there are actually different DIN fill ends for both 200 and 300bar.
The changeover device is a fixed pressure regulator, basically a scuba first stage that has an outlet pressure set to 230bar. It is a safety device and is usually used in conjunction with a pressure switch that will turn the pump off before the valve releases.
On a compressor that may be 300bar if it is filling HP bottles from Europe or bank systems, 250bar, 200bar if only filling AL80's, etc etc but all it is doing is setting that overpressure valve so the system does not build excess pressure. These OPV's are typically set a bit above the working pressure of the system. On a scuba valve it is a burst disc, on first stages it may be built in like Poseidon, be screwed into a LP port like on most argon/CCR O2 bottles, or the system will use a downstream valve like a second stage to bleed excess pressure. It is a legal requirement for safety to make sure that pressure above the working pressure of a vessel is bled so it doesn't explode. PSV is a pressure SAFETY valve and is also called a pressure relief valve/PRV or just overpressure valve/OPV. It is usually screwed into the final filter tower and then any fill whips or regulators are screwed into it as shown in the diagram you linked above The PMV is placed AFTER the filter system, but BEFORE and pressure regulating devices and whips. This is the MOST critical part of your filter system and often times the least understood. if the compressor is at 100bar, it will keep running with 0 air coming out of the whips until it hits 150bar, then once it hits 150bar, it will maintain that 150bar behind the PMV even if the tank it is filling is empty. Regulators like your first stage maintain a certain IP regardless of tank pressure, and a PMV is a backwards regulator that maintains some minimum pressure behind it and once that pressure is reached, it lets gas through. It is set somewhere around 150bar ish which maintains pressure inside of the filter stack. PMV is a pressure MAINTAINING valve and is located right after the filters. They incidentally both work in a very similar fashion in that they are downstream valves designed to maintain pressure, but they are two separate devices with very different purposes. but I have a curious mind, and I like to know everything about how stuff works Hopefully this clarifies some things. I'm probably making this a whole lot more complicated than I need to. With respect to filter tower cycles, am I better off having the changeover device, and leaving it open until I want a fill >230 bar? Or just stick with the 300bar PSV with no changeover? If I have a 300bar PSV on the filter tower, in reference to filter tower cycles, if I only fill my tanks to 220-230 bar is the compressor operating at 230 or 300bar? Even if the only time the filter will reach 300bar is when I close the tank valves to switch to the next tank, is that sufficient stress on the tower to be considered 300bar operation (I'm thinking yes, because the stress is cycles, not time at pressure) The filter tower lifetime is reduced almost 10-fold when operated at 300bar vs 225bar. The second part to my question was around the filter tower pressure cycles. if the changeover is opened, that adds a 230bar relief valve into the system, so that will blow no matter which fill hose is in use. I'm guessing it doesn't really matter where in the system the PSV is. Or does the changeover only open/close the a valve to the PSV? and following the diagram, it seems that if the changeover is closed, that also blocks off the second whip. Which seems to imply that the changeover device is attached *after* the PMV and the first hose.